Voltage and current limiter



Oct.*13, 41942. .1. E. sMn'H E-rm. y 2,293,557 v VOLTAGE AND CURRENT` LIMITER Original Filed April 27, 1939 E293 i `-Fiy6 ATTORNEY.

lPatented Oct. 134i 1942 UNlTEo s'lllflasV PATENT oFF-icl;

Vvorfrllcr AND cUaanN'r Luu'rnn originel 'application April 27, vislas, serial No. 270,332. Divided and this yapplication May 4.

- 194e, serial No. v'333,2'12

s claims. (ci. 17e-44) This invention relates toa current or voltage limiting device and is adivision Aof our application Serial No.1270,332,'1ed April 27, 1939, now Patent No. 2,257,282, issued Sept. 30, 1941.

An object of the invention is to provide an electron tube limiter using negative cut-oil' on both half -waves oi" the signal voltage, both half waves being produced by the same input coil.

Another object is to provide an improved limiter capable of maintaining a constant output with a lwidely varying input.

Other objects will appear in the following description, reference being had to the drawing in which:

Fig. 1 vis a diagrammatic illustration of the voltage limiter.

Figs. 2 to "i, inclusive, are graphs illustrating A' the operating characteristics of the limiter.

Referring `to Fig. 1,'the alternating vcurrent to be limited enters the input I of transformer 2,

to resistance 3 and the output is qonnected to the grid circuit of push-pull amplifier' i-.through transformerii. The -grid leads of thepux'sh-'pull tubes may have resistancesg 'I,x 8 to'- aid in the limiting action, but these may be omittedand the entire limiting action performed by the main limiter laterdescribed.

The outputot the push-pull amplifier-Tieren nected to, the rjectiifying device byl transformer,` I.

current f for 'each half, wave passes 'through two rectiiiers in serles and connected so that both haii' waves areiproducedby the same coil, in this case secondary- Ili, The cathodes oi' rectiilersv Il, Il

sourcl'a being'grounded.` -It is. preferable to usethisl resistance!- `I lfbutl it 'canj bejomltted ii no thresholdlimitingby the rectiilers isdesi'red.

The anode'iofs'rectiier ,Ibis/connected to the across which is connected load resistance 3. 'The Y grid circuit'of amplier 4 is adjustably connected y thence tov its cathode and to the terminal 21 of terminal 25 positive, signal current will pass from the anode sistance 2|, one end or which is connected to the positive terminal IBand the other one of whichv lis connected to negative terminal I9 through ground. This resistance is a source of vnegative bias for tubes 20 and 2I. 'I'he anodes of tubes 20 and 2| are connected in push-pull fashion and are fed from the source I8 in the usual way, asv is lindicated in the drawing.

put. Assuming that the slider I S is adjusted to the ground terminal of resistance l1 and that i resistance 26 is for the moment of tube Il to its cathode, through adjustable contact IB-to ground andJ from ground to the lower part of resistance 22, to the anode of tube I2,

will pass i'r'om the anode to the cathode oi tube I3, thence through contact I6 to ground, through the upper 'part of resistance 22, from the andde to the cathode of tube Il and thence totermiv nal 25.

- The rectifier consists ofgfourv rectiflers', I'I `I 2, i2 and I 4, which are so arranged that the rectiiled,

cathodeiof rectier Hand the-anode ofrectiiler n is connected 5to `vthe;cathode "or rejetmer I2.

The anodesor rectiilers I2 and-I4 are:connected 1 wenefgrld or 20 4allem anci1" es itaxlev 22 is thesegrids; the ,center er the beinsr'rounded. offwursafhefrrid's.

intermediate pointsptthis tnerlatefterminalsthre I ubes illgandfll arecon# denendlnsauilon teslide euntefEQM-"r-F filmer!! across thefgrid'iof; tube 2l islikeeltller orII." shapes: tllewaves. appeal-inging, aime panfiometerpre-u the output 0I the rushnunma- 2 9.-

hali of resistance 22 for one half -wave and 2 9 2the drop in theupp'erhalf for the other. half wave. lItv an oscillograph Vfor example, were placed across the whole'of resistance y22,'l it'would produce an'alternating voltage of the shape of the graph 2l, 2l.

By ending elle eentaet" le towards the peslave side or resistance l1, e 4counter' E. M. fr. is "n lmduced in therectifier circuit andthe partoit'lie wave extending `i'rom the zero axis to theflines c, d will be as lit is below thefcou'nterl j Y ME. M. F. thre shold. 1 The portion beyond thesiefg'f v win be au that is passed. 'rile fermier-tile l wave `with'tllis adjustment oisliderflwill be lines as lndicatedvat 20, 'Il Thelamounto! thresnoldaeuen een remade :desired ;1 byadjustingtllecontact'ii. y

j ,wave applied iter` In Fig. 2,y 28 represents the drop in the lower 'which places a negative bias on the grids.

Assuming for purpose of explanation that an appropriate negative bias has been placed on the grids of tubes 20 and 2| from resistance 2l, the steady electron iiow in tube 2|, that is..when no signal voltage is applied to the grid, may be of the value indicated by line B, B oi FigA and that of tube 2U by line B'. B', Fig. 5, one being reversed in reference to the other, because of the pushpull connection of the plate coils. With slider i6 on the ground end of resistance I1, the current flow through the plate circuit of tube 2l in one complete cycle ofthe signal will be indicated by graph I2 of Fig. 4. The rst half of the cycle is the reduced electron flow produced by the half wave 28 applied as a negative voltage of that tube and the last half oi the cycle o! this tube is the higher and steady electron now with no signal voltage applied to the grid.

inthe gridy ances, a source of electromotive force, each pair l of rectitlers being connected in series in a. con- During the same complete cycle the current flow in the plate circuit of tube 20 is indicated by graph 33 of Fig. 5. In both oi the graphs 32 and 33 the signal drives the grids to and below negative cut-oli, the parts of the wave cut-ott being indicated by the dotted lines. It will be apparent that the current. or voltage,` in the output circuit 36 will be a, combination of curves I2 and 33 such as is indicated by graph 3l o! Fig. 6 or graph I5 of Fig. 7, depending upon the adjustment oi slider Il on resistance I1.

The limiter oi our invention utilizes the entire input coil or transformer secondary for each half o! the wave and the input impedance of the rectiers is therefore identical, which is not true o! prior art rectiiiers. This is an important feature.

Various modificationsl may be made without departing from the spirit of our invention.

Having described our invention, what we claim is: 1. In a limiting device, input lines, a" pair oi resistances, a pair of rectiers connected together through one resistance and across said'lines to conduct current there through in one direction, a second pair of rectifiers connected together through the other resistance and across said lines ftp conduct current therethrough in the opposite direction, a connecting link between the ends oi' the resistances where theA rectified current enters therein, a pair of electron tubes having theiry cathodes connected to said link and their control electrodes connected-to points adjacent the other ends of said resistances and means for comb the output voltages of said tubes. n,

2. In a limiter for a signaling system, a signal source, two pairs of rectiers, a pair of'resistances. means for connecting each pair of rectiilers in series in a conducting circuit across said signal source through onel oi!` said resistances for full wave rectification, a"pair oi' electron tubes.

having cathodes connected to said resistances and having control electrodes connected to points in said resistances that are negative in respect t0 the connection 'of said cathodes with 'said resistances and means for combining the output voltages of said tub'es. s

3. In a limiter for asignaling system. a signal necting the junction point oi. the rectiners of one resistances and means tor combining the output voltages of said tubes in phase opposition.

4. In a limiter for a signaling system, a signal source, two pairs of rectiflers, a pair of resistances, means for connecting each pair of rectiilers together through one oi said resistances in a series conducting circuitv across said signal source for full wave rectiiication, a pair of electron tubes having cathodes joined together and connected to positive equlpotenufu points of said resistances and having their control electrodes connected toV negative equipotential points of said resistances, means ior'biasing said control electrodes negative in respect to said cathode, the negative potential thus applied to the grids being sufllcient to block the anode currents ata predetermined value of the signal potential in the resistances and means for combining the output voltages of said tubes in phase opposition.

5. In a limiting device, input terminals, a pair of rectiilers connected in a series circuit across said terminals to conduct current in one direction, a second pair of rectiers connected in a series circuit across said terminals to conduct current in the opposite direction,'a pair of vacuum tube ampliilers, means including a resistance in the mst-mentioned series circuit for impressing a negative potential 'on the input electrodes of one ampliile'r tube from the mst-mentioned current. vmeans including 'a resistance in the second-mentioned series circuit for impressing a negative potential on the input electrodes of the other amplifier tube from the second-mentioned current and means for combining the output voltages of said amplifiers.

6. In a limiting device,.input terminals, a pair of rectiners connected in a series circuit across said terminals'to conduct current in one direction,l a second pair of rectiers connected in a series circuit across said terminals to conduct current in the opposite direction, means for conpair to the junction point oi' the rectiers of the otherv pair.. a pair of vacuum tube ampliilers, means including a resistance in the rst-men-v tional series circuit tor impressing a negative l potential on the input electrodes of one ampliiler source, two pairs of rectiiiers, a. pair of resisttube from the mst-mentioned-current, means including a resistance in the second-mentioned series circuit for impressing a negative potential on the input electrodes of ltheoth'er ampliiler tube from the second-mentioned current and means for combining the output voltages of said tubesin phase opposition. v

. J. ERNEST SMITH.

JAMES N. WHITAKER.

A GILBERT R. CLARK. 

